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News on Health Professional Radio. Today is the 20th June 2014. Read by Rebecca Foster.

Scientists have taken their first look at the microscopic structure of liquid water at the coldest temperatures yet.

The study is the first step towards helping researchers explain some of the strange properties of water, which prevent oceans from freezing solid and allow fish and other aquatic life survive under ice sheets.

A team reporting in today’s issue of the journal Nature successfully took X-ray pulse images of ‘supercooled’ water, which they were able to keep liquid at temperatures of minus 46°C.

Water has many unusual physical features, which become even more striking when it’s cooled below its freezing point while still remaining liquid, a state known as supercooled.

For example, while liquids usually decrease in volume when cooled, water reaches its maximum density at 4 °C.

“Upon cooling below 4°C water expands instead of contracting,” says Professor Anders Nilsson from the Stanford University National Accelerator Laboratory.

This explains why bottles of water placed in the freezer crack.

And it also explains why ice forms on the surface of lakes, rivers and oceans in cold climates, while the liquid water below remains warmer.

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Researchers have long been interested in exploring the structure of supercooled water because its anomalous properties become amplified at low temperatures.

But to date, the onset of rapid ice crystallisation has prevented the exploration of the so-called ‘no-man’s land’ of temperatures below minus 41°C.

Nilsson and colleagues used a liquid jet to generate 10-micron sized water droplets in a vacuum, which cool rapidly as they evaporate.

For periods of just a millisecond, the researchers were able to keep droplets of water liquid down to temperatures of minus 46°C.

They then probed the structure of the droplets using a new X-ray laser generated by a particle accelerator, giving ultra-short 50 femtosecond pulses.

Nilsson and colleagues observed an accelerating transformation of the density and structure of the liquid water as temperatures approach no-man’s land.